1. Field of the Invention
This invention relates to a ferrule for a connector of an optical fiber as a terminal component for optical communication and a method of welding the ferrule and the optical fiber for joining the terminal component and the optical fiber.
2. Description of the Related Art
Generally, methods of connecting optical fibers to each other are divided broadly into two methods: one method is permanent connecting not to allow disconnecting once connecting optical fibers together; the other method is connector connecting to allow connecting and disconnecting optical fibers freely. Permanent connecting is performed by means of welding or bonding optical fibers. Connector connecting is performed by means of fitting connectors, in which one connector may be called a plug and the other connector may be called a receptacle, together to be connected physically by abutting both end faces of optical fibers.
The connector connecting has a disadvantage of larger connecting loss of optical fiber connection cause by axis misalignment or axis tilting than the permanent connecting. However, the connector connecting has an advantage of shorter time for connecting than the permanent connecting. For this reason, the connector connecting is applied extensively to connection for short-distance optical communication systems, such as domestic digital electrical equipment, home network or car network.
An optical connector for connector connecting has an optical fiber as a communication wire and a ferrule as a terminal part. The ferrule is for positioning the optical fiber in radial direction and in axial direction, and holds one end portion of the optical fiber. A method by adhesive among many methods for joining the optical fiber and the ferrule is generally used.
The method for joining the optical fiber and the ferrule with adhesive will be described herein. The optical fiber is provided with a fiber element wire having a core wire and a cladding, and a cover portion having an inner cover and an outer cover. At the end portion of the optical fiber, the fiber element wire is exposed by means of removing the cover portion.
The ferrule is formed into tubular shape. The ferrule is provide with a through hole, formed inside thereof, having a small hole portion and a large hole portion. The small hole portion is formed so as to be inserted by the fiber element wire, and the large hole portion is formed so as to be inserted by the cover portion. The end portion of the fiber element wire inserted into the small hole portion is polished to be in the same plane as the end surface of the ferrule.
The ferrule and the optical fiber can be made of various materials, for example, quartz glass or synthetic resin. The ferrule can be also made of metal or ceramic.
The cover portion of the optical fiber is coated by adhesive and the optical fiber is inserted into the ferrule. Thereafter, the optical fiber and the ferrule are fixe together by cured adhesive.
The method for joining by adhesive requires hours to cure the adhesive by heating so that productivity of optical fibers may be reduced. Furthermore, the method for joining by adhesive has drawbacks that adhesive strength may be varied correspondingly to characteristics of surfaces of the optical fibers and the ferrules, and heat resistance of joining may be low. A method for overcoming the drawback described in the Japan Patent Application Laid Open S63-137202 is known.
The aforesaid invention, as shown in FIG. 6, is to join a ferrule 60 formed with a resin capable to be ultrasonic-welded and a not-shown optical fiber having an inner cover formed with a resin capable to be ultrasonic-welded by ultrasonic welding, and does not require tension member and operation of removing cover.
The ferrule 60 includes a through hole 61 having a large hole 61a and a small hole 61b. The through hole 61 is inserted by the end of the optical fiber removed a cover portion beforehand and the small hole 61b is inserted by the fiber element wire.
A ferrule portion 60a provided with the large hole 61a has four slits 62 extending axially for absorbing a deformed portion of the ferrule 60 by ultrasonic welding.
Objects to be Solved
However, the aforesaid method for joining the optical fiber and the ferrule for the connector of the optical fiber by prior art has following drawbacks to be solved.
When pressure force of an ultrasonic welding machine is large, the slits 62 provided at the large hole 61a of the ferrule 60 may not absorb a deformed portion of the ferrule 60 by the large pressure force. If the ferrule 60 is deformed, accuracy of aligning optical axes of optical fibers is deteriorated so that optical loss of the connection is increased and optical characteristics of the connection are deteriorated.
When contact area between the through hole 61 of the ferrule 60 and the inner cover of the optical fiber is too large against requirement for joining them, heat value by friction may be increased over requirement and the heat value by friction cannot be released. Thereby, heat-affected area in a vicinity of the joining point is increased. When heat-affected area is increased, the fiber element wire, such as crystal glass or acrylic resin, has thermal stress to cause thermal stress cracking.
When contact area between the ferrule and the optical fiber is conversely small, ultrasonic vibration may be difficultly transmitted so that heating and melting of the contact area require much time to reduce productivity of the optical connector. Furthermore, joined area is small so that, when the optical fiber is pulled, the optical fiber may be stripped out backward from the ferrule.
To overcome the above drawback of prior art, an object of this invention is to provide a ferrule for a connector of an optical fiber, which can be joined in short time with the optical fiber and can position the optical fiber securely, and a method of welding the ferrule and the optical fiber.
How to Attain the Object
In order to attain the objects, a ferrule for a connector of an optical fiber, according to the present invention, having a through hole, into which one end of said optical fiber being inserted for welding, includes a plurality of projections for ultrasonic welding, said projections being provided on an inner wall of said through hole and contacted on a surface of said optical fiber.
According to the ferrule for the connector of the optical fiber mentioned above, the optical fiber is positioned radially and axially by inserting the optical fiber into the through hole of the ferrule. The optical fiber contacts on the surface of the projection of the ferrule so that displacement of the optical fiber is prevented and ultrasonic vibration is easily transmitted. Thereby, joining force of the optical fiber and the ferrule is increased.
The ferrule for the connector of the optical fiber mentioned above is further specified by that each of the projections has a circular end face.
According to the ferrule for the connector of the optical fiber mentioned above, the circular end faces of the projections can contact securely on the surface of the optical fiber.
The ferrule for the connector of the optical fiber mentioned above is further specified by that the projection is formed into a rectangular shape or a rib shape.
According to the ferrule for the connector of the optical fiber mentioned above, a contact area of the surface of the optical fiber and each of the projections is increased so that ultrasonic vibration can be easily transmitted and secure joining force can be given. Furthermore, the ferrule can be easily ejected from a molding die and moldability of the projections is improved.
The ferrule for the connector of the optical fiber mentioned above is specified by that the plurality of said projections are disposed along a circumferential direction of the inner wall of said through hole.
According to the ferrule for the connector of the optical fiber mentioned above, the plurality of joined portions of the optical fiber and the ferrule is given so that joining force of the optical fiber and the ferrule is increased.
The ferrule for the connector of the optical fiber mentioned above is specified by that the projections are disposed at equal intervals along a circumferential direction of the inner wall of said through hole.
According to the ferrule for the connector of the optical fiber mentioned above, the optical fiber is pushed uniformly from ambience so as to be radially aligned accurately in center.
The method of welding the ferrule and the optical fiber according to the present invention includes steps of inserting the optical fiber into said ferrule for the connector of the optical fiber mentioned above, and welding said projections and said optical fiber by ultrasonic vibration for joining said ferrule and said optical fiber.
According to the method of welding the ferrule and the optical fiber mentioned above, after the optical fiber is inserted into the ferrule, the ferrule is vibrated by ultrasonic wave with pressure. Thereby, the projections formed at the through hole is heated and melted by internal friction and the optical fiber and the ferrule are welded together.
The above and other objects and features of this invention will become more apparent from the following description taken in conjunction with the accompanying drawings.